The shells and endpieces that result from shearing irradiated nuclear fuel assemblies (said shearing being described in particular in patent application EP-A-0 347 312) are conventionally received in a common drum specific to this type of highly active waste, at the outlet from their respective rinsing machines. They are then encapsulated (unchanged) in a slip of cement; said slip is cast into the drum containing the waste until the drum has been filled. After welding on a safety cover, drums filled in this way are transferred directly to a storage workshop.
In order to reduce significantly the volume of concrete-covered waste that needs to be stored, it has been recommended that the shells and endpieces should be compacted. A method of compacting is described in particular in patent application WO-A-94/16449. For safety reasons, the waste can be compacted only after it has been dried and saturated in inert gas (internal inerting). The waste is compacted in a compacting canister which is preferably likewise maintained in an inert atmosphere (external inerting, around the canister inside a compacting skirt), with optimum recovery of the gases that escape. Those internal and external inerting techniques are described by the Applicant in its applications WO-A-94/15775 and FR-A-2746 054.
In this context, the Applicant is now dealing with the technical problem of drying waste prior to compacting it. As mentioned above, such prior drying is essential insofar as it is desired, during compacting, to avoid any spraying phenomenon and to limit the phenomenon of radiolysis during subsequent storage.
In said context, the Applicant has had to opt for a given drying technique performed on the waste, optionally packaged for compacting purposes.
Conventional drying techniques, in an oven or in a stream of gas are poorly adapted to the nature of the contaminated waste in question. The associated apparatus is open and does not contain means for making it easy to handle such waste which comes in pieces of relatively small size.
Given the nature of said waste, it has been decided to carry out drying in the compacting canister. This avoids handling the dry waste and volatization of dry dust having pyrophoric tendencies.
Radiation heating by means of resistance elements placed around said canister has been found to be of poor performance (the center of said canister was not heated fast enough) while heating in an oven presented the drawbacks mentioned above, so the Applicant has opted for passing a stream of hot inert gas through said waste packaged in its compacting canister; said canister has been adapted for this purpose.
Such a method of drying metallic waste that is liable to catch fire and/or explode, as described in detail below, provides good performance, is reliable, and can be implemented with total confinement.
The term “inert” is applied above to the gas as used for drying waste in accordance with the invention. Said term is repeated below in the present description and the accompanying claims, to describe said drying gas and also a sweeping gas that can be used in combination with said drying gas. This term “inert” means that the gas in question is inert with respect to the risk of catching fire and/or of explosion that exists in the present context. It does not restrict said gas to gases which are chemically inert. Gases suitable for use as a drying gas and/or a sweeping gas advantageously consist in such chemically inert gases (in particular nitrogen and argon), but can also be constituted by other gases in certain contexts, for example air when the context is drying waste based on zirconium, . . . .
Said gas for use as a drying gas and/or a sweeping gas is inert relative to the risk of pyrophoricity as it exists in any particular case.